I would imagine that if you assign the same lat/long to 2 different icons then they will be drawn in the same position and one will be over the top of the other. Try adjusting the lat/long slightly if you want to see the both icons.
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Thank you for your work around suggestion. I thought about going down this path before but thought perhaps I was missing something in the visual configuration. Particularly when James' documentation says:
This is for the scenario where there are multiple items at the same location with different categories. When off, these icons will appear on top of each other. When on, the icons will appear next to each other.
I'll try modifying the lat/long locations and see what happens.